A feature of all such processes which is relevant to the present invention is that they include compression of feed gas (i.e. the gas(es) which take part in the reaction), intermediate gas or recycle gas and generation of work by expansion of a hot process effluent or intermediate gas stream, e.g. in a power recovery turbine.
The output of the power recovery turbine may be used to provide any form of shaftwork including, but not limited to, internal process compression requirements, external compression requirements, or electrical power generation. The effluent or intermediate gas stream may undergo a temperature boost prior to entry into the power recovery turbine to increase power recovery efficiency. Whether or not this high temperature boost occurs, the processes also feature an excess of high temperature heat (as defined in the following paragraph) which cannot be accommodated in the process effluent or intermediate gas stream and which is suitable for power generation by other mechanisms (e.g. production of steam for expansion in a power recovery turbine).
To define `excess high temperature heat` it is necessary firstly to refer to `excess process heat`. This can only be defined rigorously by referring to `Pinch Technology` techniques described, for example, in `User Guide on Process Integration for the Efficient Use of Energy`, I Chem E,. Rugby, UK, 1982. There is an `excess process heat` when the combined heating capability, between the `Hot Pinch temperature` and a temperature of ambient plus .DELTA.Tmin, of process streams and reactors which require cooling to meet and/or maintain process operating conditions (i.e. the enthalpy change of the Hot Composite Curve between these two temperature levels) is greater than the combined heating requirement, between the `Cold Pinch temperature` and ambient temperature, of process sreams which require such heating to meet and/or maintain process operating conditions (i.e. the enthalpy change of the Cold Composite Curve between these two temperature levels). .DELTA.Tmin is the minimum temperature difference for heat transfer between process streams allowable for the system. This excess process heat may be used to heat so-called cooling utilities such as cooling water, air, or boiler feed water.
There is an `excess of high temperature heat` if the `excess process heat` is at a sufficiently high temperature level to allow the cooling utility to be heated so that it becomes useful for power production. For example, in the case where the cooling utility is boiler feed water, the `excess high temperature heat` would be sufficient to generate steam which could be expanded through a steam power turbine to generate useful work prevailing in the plant but may be rigorously determined by thermodynamic techniques. The most definitive and important of these techniques is Pinch Technology (or Process Integration). These particular techniques are described, for example, in "User Guide on Process Integration for the Efficient Use of Energy" I. Chem. E. Rugby, U. K., 1982.
The plants for commercial operation of all such processes are designed to operate under a so-called `full load` condition. This is the condition in which the plant is operating with either the maximum possible flow rate (compatible with the design of the plant) of feed gas to the reactor or the maximum possible production rate of products from the plant, whichever of these two criteria is economically or operationally the more beneficial. In the full load condition there will be a particular amount of feed gas required by the reactor and particular amounts of intermediate, effluent or product gases. Thus there will be a maximum amount of gas from the reaction which is available for expansion for generating work.